The way you speak has a big impact on how others perceive you. If you talk too slow you might be seen as less truthful and if you talk high-pitched you may seem nervous. Psychology Today suggests one way to correct for your natural tone and come across as credible is to use expressive speech.

The idea works regardless of how you usually speak. Psychology Today points out you just need to vary that speech a little:

Expressive speech, with modulation in pitch and volume, and a minimum of noticeable pauses, boosts credibility and enhances the impression of intelligence. Other studies show that, just as people signal the basic emotions through facial expression, we also do it through voice. Listeners instinctively detect that when we lower the usual pitch of our voice, we are sad, and when we raise it we are angry or fearful.

While you can't consciously change your voice you can pay attention to how you're speaking. If you need to sound credibile make sure you're shifting the pitch and volume around to keep people engaged with emotion.